Thread: Premium or regular unleaded?

Originally Posted by mtb_gary

I've been running regular unleaded in my '96 HSE without any problems. but I notice on a few posts some are using premium unleaded. Is this how the Thor motors are getting the better fuel consumption by paying more at the pump?

I've been using the regular unleaded on mine which too is 96 HSE and runs fine on it. I did try the 95 premium a while back, though I did notice a slight improvement in smoothness and responsiveness, I did not gain any better economy out of it. So you have to ask yourself, is it really worth spending the extra 10 cents per litre for no economic gain?

Also the Australian spec P38's are low compression motors anyway, so they really don't need the higher octane.

One thing I would not suggest using is using E10. And that is despite the VACC website telling you otherwise. The P38's are too older vehicle too gamble on the E10, eventhough they say its safe too use, you need to remember that the P38 was built before the ethanol craze, and weren't built with ethanol in mind. The newer models I.e L322 or the latest series 4 built from 2005 onwards would most likely have no issues on the E10 being a later vehicle, but not the P38. In fact I'm convinced that my fuel pump failed as a result of using the E10 previously.

sorry ..double post

FWIW The additional issue with E10 is that it can play up with the fuel gauge sender. The gauge can become erratic only ever reads half full...the only option appears to be replacement of the sender. There's a Tech Bulletin about it somewhere...

Apparently service stations don't have to advise you that they've diluted the 91 ULP with ethanol... Personally I always use 95. The extra $7 or so for an average 70L fill I reckon is worth it for the relatively low miles I drive. The engine does run more smoothly. What with the see-saw prices with a 15-20 cents /litre swing and supermarket dockets... life is too short and it's a damned side cheaper than stuffing around with bung senders.

EDIT: the energy output per unit of E10 blend is considerably less than straight ULP, so the increased fuel consumption and reduced power output in the Rover V8 which is not specially tuned for Exx blends more than offsets any cost savings

Originally Posted by Hoges

FWIW The additional issue with E10 is that it can play up with the fuel gauge sender. The gauge can become erratic only ever reads half full...the only option appears to be replacement of the sender. There's a Tech Bulletin about it somewhere...

Apparently service stations don't have to advise you that they've diluted the 91 ULP with ethanol... Personally I always use 95. The extra $7 or so for an average 70L fill I reckon is worth it for the relatively low miles I drive. The engine does run more smoothly. What with the see-saw prices with a 15-20 cents /litre swing and supermarket dockets... life is too short and it's a damned side cheaper than stuffing around with bung senders.

EDIT: the energy output per unit of E10 blend is considerably less than straight ULP, so the increased fuel consumption and reduced power output in the Rover V8 which is not specially tuned for Exx blends more than offsets any cost savings

you have to be carefull as 10% additionof ethanol is also the case with some 95 & 98 octane fuels. United do it and call it Boost 98 or 100.

But what you need to remember is that higher octane is a delay in detonation, therefor your engine management needs to make adjustments in timing to gain the full benefit of both power and economy. The trouble is a lot of people get conned into buying the high octane based on the selling methods used by oil companies cause there is a higher profit margin to be made. But what they don't tell you is the truth that not all cars need it, such a base model Holden Commodore or Ford Falcon as they are specifically tuned for running on regular 91 octane. It's not say that you can't put the higher octane in, but you won't gain anything out of it. The P38 does have I'm pretty sure a variable engine management system installed ( Please correct me if I'm wrong) so there is a little bit of performance gain to be had. But I have been informed that 95 premium is a finer fuel and therefor you do tend to use a little more, kind of equalling what you'd use in the regular stuff, but with the added performance.

I think if the fuel prices are cheap enough, I'd say buy it and trial is the best way to find out.

Yeah...I stay clear of some of the independents for that reason. Usually go for Caltex. My now departed VX Comm LS1 was tuned for 91, and went OK. SWMBO's 2005 1.8 Astra definitely performs better with 98 Octane esp on a long trip where it holds the hills in top at 95 kmh whereas on 91 it "always" drops back to 3rd...but they tell you that in the owners manual...

Thats quite true redandy. The higher the octane rating the higher the calorific value (more calories per ml), and the more calories that are to be burnt the longer this process takes, so timing needs to be advanced for higher octane fuels.

All modern cars have knock senors which detect pre-ignition (knock) so the ecu can adjust spark (and injector) timing but only to a preprogrammed amount.

Lpg is 110 octane (afaik) and the GEMS system cant advance the ignition to that amount, but it certainly can for 95, though it may take a while to advance the timing as GEMS is pretty slow.

Maybe the older vn/vp might not notice the higher octane but the d.i. motors certainly do.

Interesting discussion. I've learned a lot! Thank you to all who have contributed. As I'm not having any problems with the Caltex 91 octane I think I'll be sticking with it. Thanks once again for all your inputs, it never ceases to amaze me the knowledge database that is in this forum

One thing I have been warned is to be careful with the 98 premium as they tend to actually clog injectors on cars tuned for 91 regular. High performance cars have slightly larger nosilled injectors to prevent this, as 98 premium is more dense and of a thicker composition, where is the 95 premium is completely the opposite and finer, which may explain why some cars run better on 95 than 98. So there is another reason to read and double check your owner manual & manufacture specification to make sure that your car is suitable or let alone requires that fuel, and not to take the oil companies word.